AT&T MDC 9000 Cordless Quick Reference page 10

MDC 9000 Compatibility
MERLIN 206/410/820 systems and MERLIN Plus system
buttons should be assigned as follows; 2, 3, 4, and 5 are
line or feature buttons:
To use MERLIN LEGEND feature codes with this phone,
program the top right-hand button as a System Feature
button. This will permit you to use the wide array of
LEGEND system features by turning the set on, pressing
the System Feature button, and dialing the appropriate
"*" code number. Your cordless phone's
allows you to enter programming mode. It does not work
when using the MERLIN LEGEND system features.
MERLIN 1030/3070, MERLIN II, and MERLIN LEGEND
system buttons should be assigned as follows; 3, 4, and
5 are line or feature buttons:
[Feat]
9
button only